The present invention relates generally to data communication systems such as modem systems. More particularly, the present invention relates to the transmission of inband control signals between two modem devices having a fully digital data communication channel established therebetween.
Current modem systems are now capable of data transmission at speeds of up to 56 kilobits/second (kbps). The ITU-T Recommendation V.90 (the international standard for 56 kbps modems) currently applies to a modem system in which one modem, e.g., an internet service provider server modem, is digitally connected to the telephone network and the corresponding modem, e.g., a modem located at an end user""s personal computer, is connected to the telephone network via an analog loop. V.90 modem systems utilize pulse code modulation (PCM) techniques to accomplish the relatively high data rates that approach 56 kbps.
Although current V.90 modem systems may be suitable for most internet applications that only need to be capable of handling heavy downstream data traffic, there are some applications that can exploit the high bidirectional data rates that can be supported by a fully digital system. For example, a PBX system may include two digital modems associated with two remote end users and a fully digital communication channel defined between the modems. Similarly, it may be desirable to have two V.90 compliant server modems, each digitally connected to a telephone network, communicate with one another absent an intervening connection to an analog client modem. As another example, a digital PCM server modem can be connected to a Basic Rate ISDN modem. In such situations, it would be practical to leverage the existing encoding and other techniques utilized by digital V.90 modems to implement an effective all-digital communication channel.
While current V.90 modem systems are suitable for many applications where a relatively high downstream data rate (compared to the upstream data rate) is desired, some of the V.90 protocols may not be suitable or optimized for operation in an all-digital environment. Furthermore, assuming that an all-digital high speed modem system can be implemented, each of the digital modem devices should also be compatible with V.90 for purposes of establishing a communication session with an analog modem device. Accordingly, it would be desirable for each of the individual modem devices to be capable of determining whether or not a fully digital channel is present for a given communication session.
Conventional analog modem systems (and conventional V.90 modem systems) rely upon tonal or spectral techniques to initiate retraining, rate renegotiations, and other control procedures. Unfortunately, such techniques may not lead to optimal results in a fully digital operating mode (e.g., where both modem devices are digitally connected to a digital telephone network and no intervening analog processing is present within the communication channel) because the transmitted data has random characteristics and need not have any specifically encoded analog content. Furthermore, if tonal indicators are utilized, then actual data transmitted during a fully digital mode may be mistaken for such tonal indicators by the modem system. Accordingly, tonal or spectral indicators would not produce a robust and reliable inband control mechanism.
Accordingly, it is an advantage of the present invention that an improved control signal technique is provided for application in a fully digital data communication system.
Another advantage of the present invention is that it enables the calling and answer modems in a modem system to determine whether a fully digital communication channel has been established.
Another advantage of the present invention is that it provides a robust inband digital control channel that can be easily implemented by leveraging existing V.90 digital modem technology.
A further advantage is that the inband digital control technique can be utilized to facilitate the monitoring and maintenance of digital frame synchronization during the transmission of data.
Another advantage of the present invention is that the inband control channel may be employed to initiate modem functions such as retraining, rate renegotiations, and clear downs, and to detect signal loss.
The above and other advantages of the present invention may be carried out in one form by a data communication method for providing control signals between a first modem device and a second modem device operatively coupled together with a fully digital communication channel established therebetween. Such a method may include the steps of establishing a communication session between the first and second modem devices, executing, during the communication session, an inband signaling routine between the first and second modem devices, and conducting a control procedure during the communication session. The particular control procedure and the initiation of the control procedure is performed in response to a control signal associated with the inband signaling routine.